Neonates frequently develop iatrogenic anemia and receive transfusion of red blood cells. Many transfusion services routinely provide fresh red blood cells or washed red blood cells for all neonatal transfusions in order to decrease the potassium load associated with transfusion. We propose to monitor a cohort of newborns transfused with this product in order to determine whether transfusion of units with a high plasma potassium translates into clinically significant elevation of neonatal potassium levels.